carrier_x4.m

本文件内包含了QPSKandQAM256的系统仿真

% QPSK Demod Test

%load c:\qpsk\lecroy_1.dir\sc1000.dat;
load sc1000.dat;
offset=1;
size=1024*4;
wave=sc1000';
fs=1e9;

% Display wave form

plot(wave(1:100));
grid
title('IF Signal');
pause;

data_fft=10*log10(abs(fftshift(fft(kaiser(size,11.)'.*...
      (wave(offset:offset+size-1))))));
   data_fft=data_fft-max(data_fft);
   nnnn=size;
   ff=-nnnn/2:nnnn/2-1;
   ff=ff/nnnn*2*fs/2;
   plot(ff,data_fft);
	title(' IF Data Spectrum Before Filtering ');
	axis([400e6, 500e6 -50 0]);
	grid;
	xlabel('FREQUENCY (HZ)');
	ylabel('MAGNITUDE (dB) ');
   pause;
   
   % generate local carrier
   
   f_lo=380e6;   % carrier
   t=[0:length(wave)-1]/fs;
c_sin=sin(2*pi*f_lo*t); 	% carrier sine;
c_cos=cos(2*pi*f_lo*t); 	% carrier sine;

if_data=wave.*c_cos;	% down converting

%	% plot spectrum;
	data_fft=20*log10(abs(fftshift(fft(kaiser(size,11.)'.*...
		 if_data(offset:offset+size-1)))));
	ff=-nnnn/2:nnnn/2-1;
	ff=ff/nnnn*2*fs/2;
   plot(ff,data_fft);
	title(' I Data Spectrum After Down Converting');
	grid;
   pause;
   
   n_decimate=2;
   if_data=decimate(if_data,2);
   
   size=size/n_decimate;
   offset=10;
   
   %***************************
   %	Plot Spectrum				*
   %***************************
   
   data_fft=20*log10(abs(fftshift(fft(kaiser(size,11.)'.*...
      if_data(offset:offset+size-1)))));
   nnnn=nnnn/n_decimate;
	ff=-nnnn/2:nnnn/2-1;
	ff=ff/nnnn*2*fs/2/n_decimate;
   plot(ff,data_fft);
   axis([100e6 150e6 -10 30]);
	title(' IF Data Spectrum After Decimation');
	grid;
   pause;
   
   %************************************
   %		Design A Low-Pass Filter 		*
   %************************************
   
   f_lowpass=[   0,    115/250,   120/250 ,    1.     ];
        m=   [   1.,   1.0 ,       1e-5,       1e-5   ];

n1=80;
b=firls(n1, f_lowpass, m);
%b=fir2(n1,f_lowpass,m);
%b=fir1(n1,130/250);

a=1;
moduc=2^(-23);
%b=round(b/moduc/max(b))*moduc;
[amp,freq]=freqz(b,a,4096,fs/n_decimate);
amp=20*log10(  (abs(amp)+1e-8)  /  (max(abs(amp)) +1e-8)  );
plot(freq,amp);
grid
pause  
axis([100e6 150e6 -50 0]);
title('N1=100 taps FIR low pass filter.');
pause


if_data=filter(b,a,if_data);



   %***************************
   %	Plot Spectrum				*
   %***************************
   offset=100;
   data_fft=20*log10(abs(fftshift(fft(kaiser(size,11.)'.*...
      if_data(offset:offset+size-1)))));
	ff=-nnnn/2:nnnn/2-1;
	ff=ff/nnnn*2*fs/2/n_decimate;
   plot(ff,data_fft);
   axis([50e6 150e6 -50 30]);
	title(' IF Data Spectrum After Low-Pass Filter');
	grid;
   pause;
   
   %***************************
   %		Times 2					*
   %***************************
   
   if_data=if_data.*if_data;
   
   %***************************
   %	Plot Spectrum				*
   %***************************
   offset=100;
   data_fft=20*log10(abs(fftshift(fft(kaiser(size,11.)'.*...
      if_data(offset:offset+size-1)))));
	ff=-nnnn/2:nnnn/2-1;
	ff=ff/nnnn*2*fs/2/n_decimate;
   plot(ff,data_fft);
   axis([0e6 250e6 -50 30]);
	title(' IF Data Spectrum After X2');
	grid;
   pause;
   
   %*********************************
   %		Design A Low-Pass Filter	*
   %*********************************
   b=fir1(15,100/250,'high');

a=1;
moduc=2^(-23);
%b=round(b/moduc/max(b))*moduc;
[amp,freq]=freqz(b,a,4096,fs/n_decimate);
amp=20*log10(  (abs(amp)+1e-8)  /  (max(abs(amp)) +1e-8)  );
plot(freq,amp);
title(' High Pass Filter After X2');
grid
pause  

if_data=filter(b,a,if_data);

plot(if_data(1000:1100));
grid;
title('IF Waveform X2');
pause


   %***************************
   %		Times 4					*
   %***************************
   
   if_data=if_data.*if_data;
   
   %***************************
   %	Plot Spectrum				*
   %***************************
   offset=100;
   data_fft=20*log10(abs(fftshift(fft(kaiser(size,11.)'.*...
      if_data(offset:offset+size-1)))));
	ff=-nnnn/2:nnnn/2-1;
	ff=ff/nnnn*2*fs/2/n_decimate;
   plot(ff,data_fft);
   axis([80e6 120e6 -100 -40]);
	title(' IF Data Spectrum After X4');
	grid;
   pause;
   
   
   %*********************************
   %		Design High-Pass Filter	*
   %*********************************
   b=fir1(51,[100/250 107/250]);

a=1;
moduc=2^(-23);
%b=round(b/moduc/max(b))*moduc;
[amp,freq]=freqz(b,a,4096,fs/n_decimate);
amp=20*log10(  (abs(amp)+1e-8)  /  (max(abs(amp)) +1e-8)  );
plot(freq,amp);
title(' High Pass Filter After X2');
axis([70e6 110e6 -50 0]);
grid
pause  

if_data=filter(b,a,if_data);

plot(if_data(1100:1200),'*');
hold on;
plot(if_data(1100:1200));
hold off;
grid;
title('IF Waveform X4');
pause

%****************
%	Thresholding *
%****************

for i=1:length_if
   if if_data(i) > 0
      carrier_data(i)=1;
   else carrier_data(i)=-1;
   end
end

	%***************************
   %	Plot Spectrum				*
   %***************************
   data=carrier_data;
   offset=100;
   data_fft=20*log10(abs(fftshift(fft(kaiser(size,11.)'.*...
      data(offset:offset+size-1)))));
	ff=-nnnn/2:nnnn/2-1;
	ff=ff/nnnn*2*fs/2/n_decimate;
   plot(ff,data_fft);
   %axis([80e6 120e6 -100 -40]);
	title(' Carrier Data Spectrum');
	grid;
   pause;


carrier_data=filter(b,a,carrier_data);

plot(carrier_data(1100:1200),'*');
hold on;
plot(carrier_data(1100:1200));
hold off;
grid;
title('Carrier Waveform ');
pause


%*******************
%	Generate LO	   *
%*******************
length_if=length(if_data);
t=[0:length_if-1]/fs*n_decimate;
f_lo=100e6;


   
   
   
   
   for kk=1:200
   iq=i_data+1i*q_data;
   plot(iq(kk), '*');
   axis([-1 1 -1 1]*.2);
   grid
   %pause
   end